GB970744A - Improvements in or relating to the production of sodium sulphate or potassium sulphate - Google Patents

Abstract

<PICT:0970744/C1/1> Na2SO4 or K2SO4 is deposited upon particles of a continuously circulating stream when NaCl or KCl and H2SO4 in equivalent quantities are introduced in at least one localized region of the stream at a temperature above 350 DEG C. and below the MPt of the product Na2SO4 or K2SO4 (MPts of pure Na2SO4, K2SO4 are 884 DEG C., 1076 DEG C. respectively). The discrete identity of the circulating particles is maintained during deposition by controlling the ratio of the rate of recirculation to the rate of withdrawal of product, termed the recycle ratio, between the limits 20 : 1 and 1000 : 1. H is preferred to premix, the reactant chloride and H2SO4 to form a solution or slurry which at 20 DEG C. may contain 60% H2SO4 or at 80-120 DEG C. up to 70% H2SO4, and to introduce the solution or slurry into a reactor, e.g. a cylindrical rotating drum, within which particles of, for example, NaCl or KCl, Na2SO4 or K2SO4, are internally recirculating at 400-500 DEG C. The accompanying drawing illustrates apparatus suitable for effecting the process of the invention. A horizontal cylindrical furnace consists of a rotatable drum 1, closed at one end 2, and containing six lifting buckets 3 to raise particles and transfer them to an externally supported shoot 4, situated inside the drum and inclined downwards from the closed towards the open end of the drum. Into shoot 4 discharges a pipe 5 coming through the open and of the drum, and the furnace is heated by means of external gas burners 6. In a particular example K2SO4 particles of 1-2 mm. diameter are placed within the furnace and the drum is rotated at 20 r.p.m., causing the particles to flow down the shoot at a rate of 125 lbs. per minute. The temperature of the particles in the shoot is maintained at 460 DEG C. A slurry of 3.45 parts 54.5% H2SO4 and 2.74 parts fertilizer grade KCl is added to the shoot through 5, at a rate such as to give 1/2 lb. of product K2SO4 per minute. This represents a recycle ratio of 250 : 1. Particles are periodically removed from the recirculating stream and screened, off-size particles being returned to the reactor. The product which passes a 5 mesh B.S. sieve and is retained by a 12 mesh B.S. sieve analyses as 98.0% K2SO4, 1.3% H2SO4, 0.6% KCl. In a second example sodium sulphate is deposited at a temperature of 475 DEG C. Specification 907,900 is referred to.